The present subject matter relates generally to a drilling rig, and more particularly to a multipurpose cantilever skidding frame that can be employed in a drilling rig. The present subject matter also relates to a drilling rig having a multi-direction direct cantilever skidding system that can be employed in a Jackup drilling unit or other types of mobile platforms.
The wells to be drilled may be arranged in a grid, requiring the drilling derrick to be moved in both longitudinal and transverse directions to access the various locations of the wells. In a traditional cantilever arrangement, a Jackup drilling unit or other mobile platform may access wells through a combination of a longitudinal motion of the cantilever that skids in and out of the Jackup hull, and a transverse skidding of the drill floor at the end of the cantilever. This arrangement may be effective if the well pattern is contained within a small envelope; however, the extent to which the drill floor can skid in a transverse direction is limited. In addition, as the load is significantly offset from the cantilever center to access the side wells loads on the side of the cantilever in the direction of the offset will be increased, usually resulting in a reduced load capacity for extreme transverse drilling positions.
A cantilever skidding system allowing a cantilever to skid in both longitudinal and transverse directions is disclosed in U.S. Pat. No. 6,171,027. In this system, a drill floor is fixedly mounted to a cantilever to solve the offset problem caused by the movable Jackup drilling unit. The transverse reach of the drill floor is enabled by the transverse cantilever skidding. The cantilever is movably connected to the supporting members which are movably connected to transverse rails. The cantilever moves longitudinally over the supporting members, and the cantilever together with the supporting members move transversely over the transverse rails. The supporting members thus support the cantilever at all times and carry the full weight of the cantilever even when it is retracted. During installation, the supporting members must be accurately aligned, and then the heavy cantilever, must be lifted and slowly slid into the supporting members. Such an operation is both challenging and complex. Further, once installed the supporting members are always under load and are therefore not able to be easily accessed for inspection and maintenance.
Offshore drilling and workover rigs, for example Jackup units daily cost is much higher than land rigs. It is known that offshore rigs in development fields are assigned to drill a batch of wells from the same location using a pre-set platform. The offshore rig will jack-up with a platform next to it, then skid the rig above the platform to drill the wells. The platform will be a guide for drilling the wells and a permanent facility to complete the wells with X-trees then connected to production lines. This is achievable with the skidding system offshore rigs equipped with to be able to adjust the rig floor above require slot on platform. However, land rigs need to move the entire rig from location to another to drill wells which involves high cost, requires time, and is a high level safety operation.
An important consideration in the design and construction of workover rigs in the servicing and treatment of wells is the ability to move efficiently between wells which are located a short distance from one another, such as, for example, wells in a cluster or in one or more rows in directional drilling operations. In the past, workover rigs have been so constructed and arranged that the derrick and its substructure must be disassembled to move between each well. It has also been proposed to utilize skids without disassembling the structure but has required some disassembly of the derrick and is undesirable from a number of standpoints including but not limited to the time and cost of installation each time that the rig has to be moved. In the past such installation has involved the utilization of cables or guide wires anchored in the ground to stabilize the derrick.
Accordingly, there is a need for a portable work-over rig which does not require cables or guide wires to support or anchor the derrick and to provide for a derrick and substructure which is completely automatic and can be advanced on skids between wellheads without disassembling the derrick or other parts of the rig and can be utilized on land as well as off-shore. Further, it is desirable to construct the derrick in such a way as to facilitate mechanical side-loading and unloading of pipe from and to raised pipe rack sections at the base of the derrick without necessity of threading or loading manually upward and downward through the base of the derrick.